EP-A-0211221 discloses clamping devices for the fixed positioning of a plurality of parallel arranged optical waveguides, in which the optical waveguides are placed in a first position on a multiple tool. The clamping devices can be shifted along the multiple tool in the longitudinal and the transverse directions. They are moved in a second range for the preparation of their end faces and in a third range for the production of a welded joint. Said European Application does not disclose how the optical waveguides are threaded into the clamping devices.